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<title>Debugging with GDB: Commands In Python</title>

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<a name="Commands-In-Python"></a>
<div class="header">
<p>
Next: <a href="Parameters-In-Python.html#Parameters-In-Python" accesskey="n" rel="next">Parameters In Python</a>, Previous: <a href="Recordings-In-Python.html#Recordings-In-Python" accesskey="p" rel="previous">Recordings In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Commands-In-Python-1"></a>
<h4 class="subsubsection">23.2.2.20 Commands In Python</h4>

<a name="index-commands-in-python"></a>
<a name="index-python-commands-1"></a>
<p>You can implement new <small>GDB</small> CLI commands in Python.  A CLI
command is implemented using an instance of the <code>gdb.Command</code>
class, most commonly using a subclass.
</p>
<dl>
<dt><a name="index-Command_002e_005f_005finit_005f_005f"></a>Function: <strong>Command.__init__</strong> <em>(name, <var>command_class</var> <span class="roman">[</span>, <var>completer_class</var> <span class="roman">[</span>, <var>prefix</var><span class="roman">]]</span>)</em></dt>
<dd><p>The object initializer for <code>Command</code> registers the new command
with <small>GDB</small>.  This initializer is normally invoked from the
subclass&rsquo; own <code>__init__</code> method.
</p>
<p><var>name</var> is the name of the command.  If <var>name</var> consists of
multiple words, then the initial words are looked for as prefix
commands.  In this case, if one of the prefix commands does not exist,
an exception is raised.
</p>
<p>There is no support for multi-line commands.
</p>
<p><var>command_class</var> should be one of the &lsquo;<samp>COMMAND_</samp>&rsquo; constants
defined below.  This argument tells <small>GDB</small> how to categorize the
new command in the help system.
</p>
<p><var>completer_class</var> is an optional argument.  If given, it should be
one of the &lsquo;<samp>COMPLETE_</samp>&rsquo; constants defined below.  This argument
tells <small>GDB</small> how to perform completion for this command.  If not
given, <small>GDB</small> will attempt to complete using the object&rsquo;s
<code>complete</code> method (see below); if no such method is found, an
error will occur when completion is attempted.
</p>
<p><var>prefix</var> is an optional argument.  If <code>True</code>, then the new
command is a prefix command; sub-commands of this command may be
registered.
</p>
<p>The help text for the new command is taken from the Python
documentation string for the command&rsquo;s class, if there is one.  If no
documentation string is provided, the default value &ldquo;This command is
not documented.&rdquo; is used.
</p></dd></dl>

<a name="index-don_0027t-repeat-Python-command"></a>
<dl>
<dt><a name="index-Command_002edont_005frepeat"></a>Function: <strong>Command.dont_repeat</strong> <em>()</em></dt>
<dd><p>By default, a <small>GDB</small> command is repeated when the user enters a
blank line at the command prompt.  A command can suppress this
behavior by invoking the <code>dont_repeat</code> method.  This is similar
to the user command <code>dont-repeat</code>, see <a href="Define.html#Define">dont-repeat</a>.
</p></dd></dl>

<dl>
<dt><a name="index-Command_002einvoke"></a>Function: <strong>Command.invoke</strong> <em>(argument, from_tty)</em></dt>
<dd><p>This method is called by <small>GDB</small> when this command is invoked.
</p>
<p><var>argument</var> is a string.  It is the argument to the command, after
leading and trailing whitespace has been stripped.
</p>
<p><var>from_tty</var> is a boolean argument.  When true, this means that the
command was entered by the user at the terminal; when false it means
that the command came from elsewhere.
</p>
<p>If this method throws an exception, it is turned into a <small>GDB</small>
<code>error</code> call.  Otherwise, the return value is ignored.
</p>
<a name="index-gdb_002estring_005fto_005fargv"></a>
<p>To break <var>argument</var> up into an argv-like string use
<code>gdb.string_to_argv</code>.  This function behaves identically to
<small>GDB</small>&rsquo;s internal argument lexer <code>buildargv</code>.
It is recommended to use this for consistency.
Arguments are separated by spaces and may be quoted.
Example:
</p>
<div class="smallexample">
<pre class="smallexample">print gdb.string_to_argv (&quot;1 2\ \\\&quot;3 '4 \&quot;5' \&quot;6 '7\&quot;&quot;)
['1', '2 &quot;3', '4 &quot;5', &quot;6 '7&quot;]
</pre></div>

</dd></dl>

<a name="index-completion-of-Python-commands"></a>
<dl>
<dt><a name="index-Command_002ecomplete"></a>Function: <strong>Command.complete</strong> <em>(text, word)</em></dt>
<dd><p>This method is called by <small>GDB</small> when the user attempts
completion on this command.  All forms of completion are handled by
this method, that is, the <tt class="key">TAB</tt> and <tt class="key">M-?</tt> key bindings
(see <a href="Completion.html#Completion">Completion</a>), and the <code>complete</code> command (see <a href="Help.html#Help">complete</a>).
</p>
<p>The arguments <var>text</var> and <var>word</var> are both strings; <var>text</var>
holds the complete command line up to the cursor&rsquo;s location, while
<var>word</var> holds the last word of the command line; this is computed
using a word-breaking heuristic.
</p>
<p>The <code>complete</code> method can return several values:
</p><ul>
<li> If the return value is a sequence, the contents of the sequence are
used as the completions.  It is up to <code>complete</code> to ensure that the
contents actually do complete the word.  A zero-length sequence is
allowed, it means that there were no completions available.  Only
string elements of the sequence are used; other elements in the
sequence are ignored.

</li><li> If the return value is one of the &lsquo;<samp>COMPLETE_</samp>&rsquo; constants defined
below, then the corresponding <small>GDB</small>-internal completion
function is invoked, and its result is used.

</li><li> All other results are treated as though there were no available
completions.
</li></ul>
</dd></dl>

<p>When a new command is registered, it must be declared as a member of
some general class of commands.  This is used to classify top-level
commands in the on-line help system; note that prefix commands are not
listed under their own category but rather that of their top-level
command.  The available classifications are represented by constants
defined in the <code>gdb</code> module:
</p>
<dl compact="compact">
<dd><a name="index-COMMAND_005fNONE"></a>
<a name="index-gdb_002eCOMMAND_005fNONE"></a>
</dd>
<dt><code>gdb.COMMAND_NONE</code></dt>
<dd><p>The command does not belong to any particular class.  A command in
this category will not be displayed in any of the help categories.
</p>
<a name="index-COMMAND_005fRUNNING"></a>
<a name="index-gdb_002eCOMMAND_005fRUNNING"></a>
</dd>
<dt><code>gdb.COMMAND_RUNNING</code></dt>
<dd><p>The command is related to running the inferior.  For example,
<code>start</code>, <code>step</code>, and <code>continue</code> are in this category.
Type <kbd>help running</kbd> at the <small>GDB</small> prompt to see a list of
commands in this category.
</p>
<a name="index-COMMAND_005fDATA"></a>
<a name="index-gdb_002eCOMMAND_005fDATA"></a>
</dd>
<dt><code>gdb.COMMAND_DATA</code></dt>
<dd><p>The command is related to data or variables.  For example,
<code>call</code>, <code>find</code>, and <code>print</code> are in this category.  Type
<kbd>help data</kbd> at the <small>GDB</small> prompt to see a list of commands
in this category.
</p>
<a name="index-COMMAND_005fSTACK"></a>
<a name="index-gdb_002eCOMMAND_005fSTACK"></a>
</dd>
<dt><code>gdb.COMMAND_STACK</code></dt>
<dd><p>The command has to do with manipulation of the stack.  For example,
<code>backtrace</code>, <code>frame</code>, and <code>return</code> are in this
category.  Type <kbd>help stack</kbd> at the <small>GDB</small> prompt to see a
list of commands in this category.
</p>
<a name="index-COMMAND_005fFILES"></a>
<a name="index-gdb_002eCOMMAND_005fFILES"></a>
</dd>
<dt><code>gdb.COMMAND_FILES</code></dt>
<dd><p>This class is used for file-related commands.  For example,
<code>file</code>, <code>list</code> and <code>section</code> are in this category.
Type <kbd>help files</kbd> at the <small>GDB</small> prompt to see a list of
commands in this category.
</p>
<a name="index-COMMAND_005fSUPPORT"></a>
<a name="index-gdb_002eCOMMAND_005fSUPPORT"></a>
</dd>
<dt><code>gdb.COMMAND_SUPPORT</code></dt>
<dd><p>This should be used for &ldquo;support facilities&rdquo;, generally meaning
things that are useful to the user when interacting with <small>GDB</small>,
but not related to the state of the inferior.  For example,
<code>help</code>, <code>make</code>, and <code>shell</code> are in this category.  Type
<kbd>help support</kbd> at the <small>GDB</small> prompt to see a list of
commands in this category.
</p>
<a name="index-COMMAND_005fSTATUS"></a>
<a name="index-gdb_002eCOMMAND_005fSTATUS"></a>
</dd>
<dt><code>gdb.COMMAND_STATUS</code></dt>
<dd><p>The command is an &lsquo;<samp>info</samp>&rsquo;-related command, that is, related to the
state of <small>GDB</small> itself.  For example, <code>info</code>, <code>macro</code>,
and <code>show</code> are in this category.  Type <kbd>help status</kbd> at the
<small>GDB</small> prompt to see a list of commands in this category.
</p>
<a name="index-COMMAND_005fBREAKPOINTS"></a>
<a name="index-gdb_002eCOMMAND_005fBREAKPOINTS"></a>
</dd>
<dt><code>gdb.COMMAND_BREAKPOINTS</code></dt>
<dd><p>The command has to do with breakpoints.  For example, <code>break</code>,
<code>clear</code>, and <code>delete</code> are in this category.  Type <kbd>help
breakpoints</kbd> at the <small>GDB</small> prompt to see a list of commands in
this category.
</p>
<a name="index-COMMAND_005fTRACEPOINTS"></a>
<a name="index-gdb_002eCOMMAND_005fTRACEPOINTS"></a>
</dd>
<dt><code>gdb.COMMAND_TRACEPOINTS</code></dt>
<dd><p>The command has to do with tracepoints.  For example, <code>trace</code>,
<code>actions</code>, and <code>tfind</code> are in this category.  Type
<kbd>help tracepoints</kbd> at the <small>GDB</small> prompt to see a list of
commands in this category.
</p>
<a name="index-COMMAND_005fTUI"></a>
<a name="index-gdb_002eCOMMAND_005fTUI"></a>
</dd>
<dt><code>gdb.COMMAND_TUI</code></dt>
<dd><p>The command has to do with the text user interface (see <a href="TUI.html#TUI">TUI</a>).
Type <kbd>help tui</kbd> at the <small>GDB</small> prompt to see a list of
commands in this category.
</p>
<a name="index-COMMAND_005fUSER"></a>
<a name="index-gdb_002eCOMMAND_005fUSER"></a>
</dd>
<dt><code>gdb.COMMAND_USER</code></dt>
<dd><p>The command is a general purpose command for the user, and typically
does not fit in one of the other categories.
Type <kbd>help user-defined</kbd> at the <small>GDB</small> prompt to see
a list of commands in this category, as well as the list of gdb macros
(see <a href="Sequences.html#Sequences">Sequences</a>).
</p>
<a name="index-COMMAND_005fOBSCURE"></a>
<a name="index-gdb_002eCOMMAND_005fOBSCURE"></a>
</dd>
<dt><code>gdb.COMMAND_OBSCURE</code></dt>
<dd><p>The command is only used in unusual circumstances, or is not of
general interest to users.  For example, <code>checkpoint</code>,
<code>fork</code>, and <code>stop</code> are in this category.  Type <kbd>help
obscure</kbd> at the <small>GDB</small> prompt to see a list of commands in this
category.
</p>
<a name="index-COMMAND_005fMAINTENANCE"></a>
<a name="index-gdb_002eCOMMAND_005fMAINTENANCE"></a>
</dd>
<dt><code>gdb.COMMAND_MAINTENANCE</code></dt>
<dd><p>The command is only useful to <small>GDB</small> maintainers.  The
<code>maintenance</code> and <code>flushregs</code> commands are in this category.
Type <kbd>help internals</kbd> at the <small>GDB</small> prompt to see a list of
commands in this category.
</p></dd>
</dl>

<p>A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it
from the <code>complete</code> method.  These predefined completion
constants are all defined in the <code>gdb</code> module:
</p>
<dl compact="compact">
<dd><a name="index-COMPLETE_005fNONE"></a>
</dd>
<dt><code>gdb.COMPLETE_NONE</code>
<a name="index-gdb_002eCOMPLETE_005fNONE"></a>
</dt>
<dd><p>This constant means that no completion should be done.
</p>
<a name="index-COMPLETE_005fFILENAME"></a>
</dd>
<dt><code>gdb.COMPLETE_FILENAME</code>
<a name="index-gdb_002eCOMPLETE_005fFILENAME"></a>
</dt>
<dd><p>This constant means that filename completion should be performed.
</p>
<a name="index-COMPLETE_005fLOCATION"></a>
</dd>
<dt><code>gdb.COMPLETE_LOCATION</code>
<a name="index-gdb_002eCOMPLETE_005fLOCATION"></a>
</dt>
<dd><p>This constant means that location completion should be done.
See <a href="Specify-Location.html#Specify-Location">Specify Location</a>.
</p>
<a name="index-COMPLETE_005fCOMMAND"></a>
</dd>
<dt><code>gdb.COMPLETE_COMMAND</code>
<a name="index-gdb_002eCOMPLETE_005fCOMMAND"></a>
</dt>
<dd><p>This constant means that completion should examine <small>GDB</small>
command names.
</p>
<a name="index-COMPLETE_005fSYMBOL"></a>
</dd>
<dt><code>gdb.COMPLETE_SYMBOL</code>
<a name="index-gdb_002eCOMPLETE_005fSYMBOL"></a>
</dt>
<dd><p>This constant means that completion should be done using symbol names
as the source.
</p>
<a name="index-COMPLETE_005fEXPRESSION"></a>
</dd>
<dt><code>gdb.COMPLETE_EXPRESSION</code>
<a name="index-gdb_002eCOMPLETE_005fEXPRESSION"></a>
</dt>
<dd><p>This constant means that completion should be done on expressions.
Often this means completing on symbol names, but some language
parsers also have support for completing on field names.
</p></dd>
</dl>

<p>The following code snippet shows how a trivial CLI command can be
implemented in Python:
</p>
<div class="smallexample">
<pre class="smallexample">class HelloWorld (gdb.Command):
  &quot;&quot;&quot;Greet the whole world.&quot;&quot;&quot;

  def __init__ (self):
    super (HelloWorld, self).__init__ (&quot;hello-world&quot;, gdb.COMMAND_USER)

  def invoke (self, arg, from_tty):
    print &quot;Hello, World!&quot;

HelloWorld ()
</pre></div>

<p>The last line instantiates the class, and is necessary to trigger the
registration of the command with <small>GDB</small>.  Depending on how the
Python code is read into <small>GDB</small>, you may need to import the
<code>gdb</code> module explicitly.
</p>
<hr>
<div class="header">
<p>
Next: <a href="Parameters-In-Python.html#Parameters-In-Python" accesskey="n" rel="next">Parameters In Python</a>, Previous: <a href="Recordings-In-Python.html#Recordings-In-Python" accesskey="p" rel="previous">Recordings In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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